Set gypsum (i.e., calcium sulfate dihydrate) is a well-known material that is used in many products, including panels and other products for building construction and remodeling. One such panel (often referred to as gypsum board) is in the form of a set gypsum layer sandwiched between two cover sheets (e.g., paper-faced board) and is commonly used in drywall construction of interior walls and ceilings of buildings. One or more dense layers, often referred to as “skim coats” may be included on either side of the core, usually at the paper-core interface.
During manufacture of the board, stucco (i.e., calcined gypsum in the form of calcium sulfate hemihydrate and/or calcium sulfate anhydrite), water, and other ingredients as appropriate are mixed, typically in a pin mixer as the term is used in the art. A slurry is formed and discharged from the mixer onto a moving conveyor carrying a cover sheet with one of the skim coats (if present) already applied (often upstream of the mixer). The slurry is spread over the paper (with skim coat optionally included on the paper). Another cover sheet, with or without skim coat, is applied onto the slurry to form the sandwich structure of desired thickness with the aid of, e.g., a forming plate or the like. The mixture is cast and allowed to harden to form set (i.e., rehydrated) gypsum by reaction of the calcined gypsum with water to form a matrix of crystalline hydrated gypsum (i.e., calcium sulfate dihydrate). It is the desired hydration of the calcined gypsum that enables the formation of the interlocking matrix of set gypsum crystals, thereby imparting strength to the gypsum structure in the product. Heat is required (e.g., in a kiln) to drive off the remaining free (i.e., unreacted) water to yield a dry product.
One benefit of using gypsum in wallboard is that gypsum has a natural fire resistance property. Should the finished gypsum board be exposed to relatively high temperatures, such as those produced by high temperature flames or gases, portions of the set gypsum layer may absorb sufficient heat to start the release of water from the gypsum dihydrate crystals of the core. The absorption of heat and release of water from the gypsum dihydrate may be sufficient to retard heat transmission through or within the panels for a time. Gypsum board may experience shrinkage of the panel dimensions in one or more directions as one result of some or all of these high temperature heating effects, and such shrinkage may cause failures in the structural integrity of the board.
Some gypsum board products are designed to have enhanced fire resistance as compared with the property of the set gypsum alone. For example, Type X board refers to a type of fire rated board gypsum board, such as SHEETROCK® Brand FIRE CODE® Type X board. One example of an additive that enhances the fire resistance of gypsum board is high expansion vermiculite, which can be included in the gypsum slurry for forming the gypsum board, as described in, e.g., U.S. Pat. No. 8,323,785. One drawback is that such vermiculite can be in short supply. Thus, there is a need for alternative fire resistance additives.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as a reference to prior art nor as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some regards and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims, and not by the ability of any embodiments of the disclosure to solve any specific problem noted herein.